1. Mating:
- Planarians are hermaphrodites, meaning they possess both male and female reproductive systems.
- Two planarians align their ventral surfaces and exchange sperm through the male ducts during copulation.
2. Formation of Gametes:
- Within each planarian, the ovaries produce eggs, while the testes produce sperm.
3. Egg-laying:
- Following copulation, each planarian lays fertilized eggs, encased in protective cocoons, into the environment. These cocoons may be deposited on various substrates like aquatic plants, rocks, or even in damp soil.
4. Embryonic Development:
- Inside the cocoons, the fertilized eggs undergo embryonic development over time.
5. Hatching:
- Eventually, juvenile planarians emerge from the cocoons as fully formed miniature versions of the adults. The exact duration of development may vary depending on the species and environmental conditions.
It's worth noting that not all flatworm species reproduce sexually. Some may utilize asexual reproduction, such as by fragmentation or budding, where new individuals develop from fragments of the parent's body. However, sexual reproduction allows for genetic recombination, increasing genetic diversity in the population and playing a significant role in species adaptation and survival.